There are 435 seats in Congress, which are redistributed every 10 years after the national census.

This year`s census shows that during the 1980s, the number of Illinois residents essentially held steady while some other states were booming. As a result Illinois will lose two House seats.

But which two?

On a statistical basis, one would be likely from among the three west-central congressional districts represented by Democrats Lane Evans and Richard Durbin and Republican Robert Michel, the House minority leader.

The other would likely be from among the eight districts that are dominated by Chicago. The region appears to have suffered a decline in population-as much as 9 percent, according to the early numbers.

But although there are clear-cut rules and formulas for determining how many representatives each state has in Congress, the process of distributing them is, by design, open to political artistry.

This enables the political party in control of state legislatures to dominate the process and draw new boundaries to its advantage.

Ten years ago, when Illinois lost two congressional seats, it was statistically clear that one would have to come from the Chicago area because the city had lost 360,000 people during the 1970s.

But when the new map was produced by the Democrats-surprise-the losers were two suburban Republicans whose districts evaporated, even though the six- county suburban area had grown by nearly half a million people during the previous decade.

The odds are that after this year`s election, the Democrats will again hold majorities in the Illinois House and Senate, and their control will be even stronger if the party standard-bearer, Neil Hartigan, defeats Republican Jim Edgar in the governor`s race.

Still, in the redistricting wars little is certain. Blacks and Hispanics have begun organizing to have their say in the map-drawing, and lawsuits are likely.